According to the document of IEEE Intelligent Vehicles Symposium, October 2000, “Real-Time Stereo Vision for Urban Traffic Scene Understanding”, U. Franke, one may record the surroundings of a vehicle using an image recording unit, which includes a stereo camera for taking three-dimensional images. By evaluating the scene taken, the position of, for example, additional vehicles, persons or objects in the surroundings of the vehicle may be ascertained. In the light of this information, the longitudinal and/or lateral guidance of the vehicle may be influenced by a controller, so that the driver may be supported in his vehicle guidance, and driving comfort and traffic safety may be improved. For example, in the case of a threatening collision, an automatic evasive maneuver or braking maneuver may avoid the collision or at least reduce the collision energy.
According to MIT Press document, 1995, “Three-Dimensional Computer Vision: A Geometric Viewpoint”, O. Faugeras, a stereo camera system may ascertain a three-dimensional geometry of the surroundings projected onto the image pair by triangulation, i.e., by determining the intersection of the light beams falling into the left and right camera, respectively. Thereby it may be established that the position of the camera heads, that is, the alignment of their optical axes, of a stereo camera considerably influences the detecting properties, and many objects make stereo-sensing more difficult on account of their position or texture.
The choice of the optical focal length of a rigid stereo set-up may require a compromise between operating range and viewing angle. In vehicle applications, however, high requirements may be set for both variables. Thus, in the case of travel speeds of ca. 200 km/h, an operating range of more than 100 m may be required, for example, according to the so-called “half tachometer rule”. At the same time, a reliable recording of traffic signs may require large viewing angles, such as, for example, 70°. These requirements may not be met using other stereo cameras.
As a remedy, IEEE Intelligent Vehicles Symposium, October 2000, “EMS Vision: Gaze Control in Autonomous Vehicles”, M. Pellkofer and E. D. Dickmanns, discusses that one may mount individual mono-cameras having different focal lengths on a rotatable platform to widen the recordable viewing angle. In this connection, the camera platform may be aligned with a distant object or with an object that is present laterally to the travel direction, such as a traffic sign.